add _vercel for verification

domains/_vercel.zulnv.json

@@ -0,0 +1,9 @@
+{
+  "owner": {
+    "username": "vietdung97",
+    "email": "ngovietdung0112@gmail.com"
+  },
+  "records": {
+    "TXT": ["vc-domain-verify=zulnv.is-a.dev"]
+  }
+}